This invention relates generally to the field of fabrication, and particularly to the filed of microfabrication.
Products constructed using conventional technology are generally built using a xe2x80x9ctop-downxe2x80x9d approach. Top-down refers to the current way of fabricating most of today""s products, using large and expensive machines to manipulate matter in bulk. While miniaturization of devices using top-down technology has increased performance and efficiency, the use of top-down technology to miniaturize devices becomes increasingly difficult and expensive with the decrease in the size of the fabricated object. For instance, conventional techniques for etching circuit patterns, particularly in microcircuits, it is difficult to carry out stable and uniform etching methods when the printed circuits have a width of 0.1 mm or less.
An alternative to top-down technology, a so-called xe2x80x9cbottom-upxe2x80x9d approach, refers to the fabrication of objects from a set of small, fundamental building blocks, which cannot be reduced further. Complex objects are fabricated by creating and assembling these building blocks using a specified sequence of construction steps. This technique is very similar to creating software, where the building blocks of information (bits) are arranged in useful patterns.
Molecular assembly presents a xe2x80x98bottom-upxe2x80x99 approach to the fabrication of objects specified with incredible precision. Molecular assembly includes construction of objects using tiny assembly components, which can be arranged using techniques such as microscopy, e.g. scanning electron microspray. Microelectrodeposition and microetching can also be used in microfabrication of objects having distinct, patterned surfaces.
Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions as small as 1 to 100 nanometers, and having molecular weights of 104 to 1010 daltons. Structures even in the upper portion of this range of sizes are presently difficult to attain through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication. G M Whitesides et al., Science 254:1312-9 (1991).
Regular arrays of topologically complex, millimeter-scale objects can also be prepared by self-assembly, with the shapes of the assembling objects and the wettability of their surfaces determining the structure of the arrays. N. Bowden et al., Science 276:233-5 (1997). DNA molecular structures and intermolecular interactions are particularly amenable to the design and synthesis of complex molecular objects, and it has been shown that two-dimensional crystalline forms of DNA can self-assemble from synthetic DNA double-crossover molecules. E Winfree et al., Nature, 39453944 (1998).
There is a need in the art for a systematic and reproducible method of providing structural components for the fabrication of small objects. There is also a need in the art for a method of modifying very small objects by the directed placement of particles.
Atomized particles (which may be solid or hollow spheres) within a desired size range (e.g., 0.001 to 100 microns) are produced from a supercritical flow created by two immiscible fluids, a first fluid source containing the formulation to be atomized, and a second fluid source which is contained in a pressure chamber surrounding at least the area where the first liquid is to be provided. Upon presentation of the first fluid source to the second, the second fluid is forced out of an opening positioned in front of the flow path of the formulation. Supercritical flow is obtained when the first and second fluids interact dynamically to form a stable capillary microjet, which in turn results in the formation of a focusing funnel at the opening. Formulation passing through the focusing funnel will atomize upon exiting the opening of the pressurized chamber without physically contacting the perimeter of the opening.
In a first embodiment, the first fluid is forced through a single channel of a feeding needle and expelled out of an exit opening of the needle. The second fluid is forced out of an opening directly in front of the flow path of the formulation being expelled from the feeding needle.
One object of the invention is the production of templates for microfabrication, such as particles that serve as templates for self-assembly of monolayers, the first fluid is preferably a liquid, the second fluid is preferably a liquid immiscible with the first, and the particles are preferably expelled into a liquid that is the same or similar to the second liquid. This creates particles that are suspended in the second fluid, and the liquid interface of the particles provides a surface for the action of microcapillary forces.
Another object of the invention is the creation of small particles to serve as building blocks for the microassembly of objects. One type of particle that may be particularly useful are small, hollow particles composed of a gas nucleus, preferably an air nucleus, and a solid coating.
Another object of the invention is to create an array of small particles using the method of the invention. Particles containing a relatively constant concentration of materials, and conformity of size (e.g. 3 to 30% difference in diameter) from particle to particle, may be dispersed on any appropriate solid support surface.
Another object of the invention is to create particles which each contain a constant amount of a discrete molecule. Such discrete molecules are preferably biological molecules, informatics molecules, and/or energy conversion molecules.
Another object of the invention is liquid is preferably a solution containing a high concentration of solute. Alternatively, the first fluid liquid is a suspension containing a high concentration of suspended matter. In either case, the liquid quickly evaporates upon atomization (due to the small size of the particles formed) to leave very small dry particles.
In a second embodiment of the invention, the first fluid is comprised of a plurality of fluids that are forced through separate channels and expelled out of an exit opening of the needle. The stream of the different fluids contact prior to being expelled to creating a plurality of layers to be atomized. The second fluid is forced out of an opening directly in front of the flow path of the fluids being expelled from the feeding needle.
A feature of the invention is that the method can produce particles each of which are comprised of a plurality of formulations.
An object of the invention is the creation of particles having multiple layers which contain discrete molecules. Such discrete molecules may be present in any of the layers of the formulation, but preferably are within the innermost layer. The discrete molecules may be dissolved or suspended in a liquid, or may be suspended or sublimated in a gas.
In yet a third embodiment of the invention, a planar feeding piece is used to obtain multiple microjets which are expelled through multiple exit ports of a pressure chamber to create multiple atomized streams.
A feature of the invention is that the diameter of the opening from which the fluid is expelled, the diameter of the opening from which gas is expelled, and the distance between these two openings is adjustable to obtain a stable liquid-gas interface which results in a supercritical flow creating a stable capillary jet between the gas and the liquid.
An aspect of the invention is a device and method which produces multiple streams of atomizate thereby quickly atomizing a large amount of formulation.
Another aspect of the invention is the use of an atomizate to etch configurations and/or patterns onto the surface of an object by removing a selected portion of the surface, e.g. to removal of a film coating (i.e. copper) from the surface of a circuit board.
An object of the invention is to provide a method of creating particles of consistent particle size.
Another object of the invention is to provide particles suitable for use in fabrication assembly.
An advantage of the invention is that it consistently produces particles within a desired particle diameter range.
Another advantage of the invention is that the device of the invention is energy efficient in terms of the energy used to create small particles.
Another advantage of the invention is that the method of the invention does not impose size limitations of other methods of creating particles found in the art.
Another advantage of the invention is that it can produce large quantities of particles while expending relatively little energy.
Another advantage of the invention is that the opening from which the fluid is expelled does not accumulate deposits of the formulation.
Another advantage of the invention is that the particles are not prone to agglomeration following dispersion from the opening of the pressure chamber.
Another advantage is that the structure of the device and its use are simple.